U.S. patent application number 14/074064 was filed with the patent office on 2014-05-15 for wireless data exchange in a network comprising collaborative nodes.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. The applicant listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Patrice NEZOU, Pascal VIGER.
Application Number | 20140133495 14/074064 |
Document ID | / |
Family ID | 47470377 |
Filed Date | 2014-05-15 |
United States Patent
Application |
20140133495 |
Kind Code |
A1 |
VIGER; Pascal ; et
al. |
May 15, 2014 |
WIRELESS DATA EXCHANGE IN A NETWORK COMPRISING COLLABORATIVE
NODES
Abstract
The method improves data exchange on a wireless communication
medium accessible by a plurality of nodes via a contention
mechanism, the plurality of nodes comprising legacy nodes and a
collaborative group of nodes, each node of the collaborative group
being provided with a first and a second MAC address. The method
comprises, upon successful contention at a first node of the group,
at the first node: determining if a communication from a source
node of the group to a legacy node is required, and in such a case,
selecting the second MAC address of the source node as source
address for issuing a request to access the medium (RTS), and, upon
reception of a medium access authorization (CTS): transmitting
first data to the legacy node using said second MAC address, and
transmitting second data inside the group using said first MAC
address.
Inventors: |
VIGER; Pascal; (Janze,
FR) ; NEZOU; Patrice; (St Sulpice La Foret,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
47470377 |
Appl. No.: |
14/074064 |
Filed: |
November 7, 2013 |
Current U.S.
Class: |
370/442 |
Current CPC
Class: |
H04W 74/0816
20130101 |
Class at
Publication: |
370/442 |
International
Class: |
H04W 74/08 20060101
H04W074/08 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 9, 2012 |
GB |
1220234.7 |
Claims
1. A method of data exchange on a wireless communication medium
accessible by a plurality of nodes via a contention mechanism, the
plurality of nodes comprising a collaborative group of nodes, each
node of the collaborative group being provided with a first and a
second MAC address, and, upon successful contention at a first node
of the group, the method comprising at the first node: determining
if a communication from a source node of the group to a node
outside the group is required, and in such a case, selecting the
second MAC address of the source node as source address for issuing
a request to access the medium (RTS), the method further
comprising, transmitting first data from the source node to the
node outside the group using said second MAC address as a source
address, transmitting second data from the first node inside the
group using its first MAC address as a source address.
2. The method of claim 1 wherein the first node is the source
node.
3. A method of data exchange on a wireless communication medium
accessible by a plurality of nodes via a contention mechanism, the
plurality of nodes comprising a collaborative group of nodes, each
node of the collaborative group being provided with a first and a
second MAC address, and, upon detection by a second node of the
group of a medium access request containing a second MAC address as
source node address or a medium access authorization containing a
second MAC address as destination node address, the method
comprising: transmitting first data from a source node to a node
outside the group using said second MAC address as a source
address, and transmitting second data from the second node inside
the group using its first MAC address as a source address.
4. The method of claim 3 wherein the second node is the source
node.
5. The method of claim 1 wherein the transmitting of the second
data is realized from at least one node of the group to another
node of the group.
6. The method of claim 1 wherein a time slot is requested by a
medium access request (RTS) and granted upon a medium access
authorization (CTS), the first and second transmission being
realized within the granted time slot.
7. The method of claim 6 wherein the first data transmission is
separated from the second data transmission by a short control
frame.
8. The method of claim 7 wherein the short control frame
communicates to the nodes of the group the time remaining from the
granted time slot for the second data transmission.
9. The method of claim 7 wherein a MAC address used as destination
address of the short control frame is changed to the first MAC
address of a node of the collaborative group.
10. The method of claim 1 wherein upon detection of a medium access
request or authorization containing a second MAC address as a
source address, at least one node of the group prepares second data
to be transmitted inside the group in the said allocated time
slot.
11. The method of claim 1 wherein upon detection of a medium access
request or authorization containing a second MAC address, the node
having the second MAC address prepares first data to be transmitted
to the node outside the group.
12. The method of claim 1 wherein the first MAC address is used to
communicate exclusively inside the group of nodes or exclusively
outside the group whereas the second MAC address is used to
combined communication inside and outside the group of nodes.
13. The method of claim 1 wherein the first address and second MAC
addresses of the node of the group are representative of a same
Media Access Control (MAC) entity.
14. The method of claim 1 wherein the first and second MAC
addresses are identified by managing a universally/locally bit.
15. The method of claim 1 wherein all the first and second MAC
addresses are exchanged and/or stored among the collaborative
group.
16. The method of claim 1 wherein the plurality of nodes implement
a back-off counting procedure to access the wireless medium, and
the collaborative group of nodes implements a synchronized back-off
counting such that each node of the group has a distinct back-off
value.
17. The method of claim 16 wherein the back-off counting is
synchronized in each node of the group by managing a list of
back-off values of the nodes of the group.
18. A non-transitory computer readable medium storing a computer
program comprising instructions for carrying out the method
according to claim 1.
19. A node for data exchange on a wireless communication medium
accessible by a plurality of nodes via a contention mechanism, the
plurality of nodes comprising a collaborative group of nodes, each
node of the collaborative group being provided with a first and a
second MAC address, the node comprising: a back-off management
module for detecting a successful contention, a RTS/CTS module for
determining if a communication from a source node of the group to a
node outside the group is required, a MAC address management module
for switching between the first and the second MAC addresses of the
source node as source address for issuing a request to access the
medium by the RTS/CTS module, according to the determination of the
RTS/CTS module.
20. A node for data exchange on a wireless communication medium
accessible by a plurality of nodes via a contention mechanism, the
plurality of nodes comprising a collaborative group of nodes, each
node of the collaborative group being provided with a first and a
second MAC address, the node comprising: a RTS/CTS module for
detecting a first or second MAC address type in a medium access
request as source node or in a medium access authorization as
destination node address, a data transmission module for:
transmitting first data to a node outside the group using the
second MAC address, and transmitting second data inside the group
using the first MAC address.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(a)-(d) of United Kingdom Patent Application No.
1220234.7, filed on Nov. 9, 2012 and entitled "Method, device
computer program and information storage means for wireless data
exchange in a network comprising collaborative nodes".
[0002] The above cited patent application is incorporated herein by
reference in its entirety.
FIELD OF THE INVENTION
[0003] The invention lies in the technical field of wireless
communication networks.
[0004] The invention pertains to optimizing data exchanges in a
wireless communication network using Carrier Sense Multiple Access
with Collision Avoidance (CSMA/CA), the network being accessible by
a plurality of nodes.
BACKGROUND OF THE INVENTION
[0005] Wireless local area networks (WLANs), such as a wireless
medium in a communication network using Carrier Sense Multiple
Access with Collision Avoidance (CSMA/CA), are founded on the
principles of collision avoidance. Such networks may also conform
to a communication standard such as a communication protocol of
802.11 type e.g. Medium Access Control (MAC). The collision
avoidance approach aims to separate concurrent transmissions in
space and time. Packets of e.g. data are corrupted due to collision
or channel fading. The transmitter remains unaware of the
corruption and continues to transmit the entire packet
unnecessarily. Eventually, based on the absence of an
acknowledgment from the receiver, the transmitter infers packet
loss, and prepares for retransmission.
[0006] The IEEE 802.11 standard defines the way WLANs must work at
the physical and medium access control (MAC) level. Typically, the
802.11 MAC (Medium Access Control) relies on a contention-based
mechanism based on a technique called "Carrier Sense Multiple
Access with Collision Avoidance" (CSMA/CA). The standard 802.11
medium access protocol is essentially to wait for the medium to
become idle.
[0007] Carrier sensing is performed by both physical and virtual
mechanisms. The virtual carrier sensing is achieved by transmitting
control packets to reserve the medium prior to transmission of data
packets. The transmitter attempts to sense an idle medium for at
least a DIFS (distributed interframe spacing) duration of time. If
the medium is sensed busy, the transmitter waits until it becomes
idle and then starts a countdown back-off timer set to expire after
a number of slot times, chosen randomly between [0,CW] (i.e. the
contention window CW being an integer value).
[0008] More precisely, the period of back-off timer countdown is
called the `back-off procedure`, and is implemented as follows:
Upon starting the back-off process, prior to data transmission, a
station initializes its back-off time counter to a `random value`.
The back-off time counter is decremented once every time interval
for so long as the channel is sensed to be idle (e.g. with
reference to FIG. 1, count down starting from T0), halted (or
frozen) when a transmission is detected on the channel (e.g. with
reference to FIG. 1, count down stopping at T1), and reactivated
when the channel is sensed idle again (e.g. with reference to FIG.
1, T2). When its back-off time counter reaches zero, a station
transmits a DATA message (or ready-to-send (RTS) message as
explained hereafter) which contains the address of the receiver and
the duration for which the medium is to be reserved for that
message. A collision occurs when two or more stations start
transmission simultaneously (e.g. when their own back-off counter
has reached zero around the same time). Ideally, the same number of
slots is present among all nodes forming the 802.11 cell during the
back-off countdown procedure.
[0009] Since the CSMA/CA protocol does not rely on the capability
of the stations to detect a collision by hearing their own
transmission, a positive acknowledgement (ACK) is transmitted by
the destination station to signal the successful packet reception.
The ACK is immediately transmitted at the end of the packet, after
a period of time called Short InterFrame Space (SIFS). If the
transmitting station does not receive the ACK within a specified
ACK Timeout, or it detects the transmission of a different packet
on the channel, it reschedules the packet transmission according to
the given back-off rules.
[0010] Collision Avoidance is more specifically enhanced by a
four-way handshaking mechanism called RTS/CTS
(request-to-send/clear-to-send) exchange, which is a recommended
option of the 802.11 standard, and will be detailed with reference
to FIG. 1.
[0011] US patent application 2009/0141738 A1 discloses a time slot
system where a back-off counter value determination engine selects
an unreserved time slot for a next transmission and a medium access
engine for initiating a current transmission. This document uses a
reservation-based distributed collision avoidance channel access in
a wireless area network. By advertising the future channel access
parameters in advance, nodes reduce the number of collisions.
However, any extra functionality devised to maintain the
reservation procedure adds overhead to the functioning of the
device and consumes more bandwidth, both situations being very
undesirable.
[0012] The present inventors have therefore envisaged using a
collaborative medium access scheme for several nodes at a time,
those nodes pertaining to a group of peer nodes, also called
collaborative nodes. It is envisaged that there will also exist
nodes outside of the collaborative group, and that communication
between nodes inside and nodes outside the group may be required.
Nodes outside the group may be referred to as legacy nodes. A
legacy environment typically describes a situation where nodes are
independent and do not interact or cooperate with each other, as
opposed to the collaborative group of nodes. A peer node may
request access to the shared 802.11 type medium according to the
802.11 legacy protocol, and upon grant of access, the node may
communicate with one or more peer nodes according to a
collaborative protocol during the reserved talk time. Thus, if the
back-off count reduces to zero for one peer node among the group,
said node reserves medium access (through classical RTS/CTS scheme)
for the group and lets the group share this granted 802.11
timeslot.
A collaborative node can either communicate inside the group via
the collaborative access scheme, or it communicates with legacy
nodes outside the collaborative group using the 802.11 legacy
protocol: thus no mixed mode is supported which would allow a
collaborative node to communicate indifferently with peer nodes and
legacy node. Indeed, the collaborative group has no mean to know
the communication timeslot which is going to be granted to a
collaborative node for a legacy communication, which prevents a
collaborative group communication to take place (as example a "time
division multiple access", aka TDMA, communication). Therefore, a
collaborative medium access scheme, like for example a distributed
back-off mechanism, does not allow communicating with legacy nodes,
except by leaving the collaborative sub-network, then eventually
joining again after completing the data transmission with the
legacy.
[0013] Thus aforementioned problems are limiting the optimal
functioning of a wireless network.
SUMMARY OF THE INVENTION
[0014] It would be desirable, in particular, to improve the ability
to communicate between legacy and collaborative nodes in a wireless
communication network while also minimizing the overhead introduced
for such a communication.
According to one aspect of the invention there is provided a method
of data exchange on a wireless communication medium accessible by a
plurality of nodes via a contention mechanism, the plurality of
nodes comprising a collaborative group of nodes, each node of the
collaborative group being provided with a first and a second MAC
address, and, upon successful contention (i.e. the back-off
counting of the node reaches zero) at a first node of the group,
the method comprising at the first node:
[0015] determining if a communication from a source node of the
group to a node outside the group is required, and in such a
case,
[0016] selecting the second MAC address of the source node as
source address for issuing a request to access the medium
(RTS),
the method further comprising,
[0017] transmitting first data from the source node to the node
outside the group using said second MAC address as a source
address,
[0018] transmitting second data from the first node inside the
group using its first MAC address as a source address.
The method allows a source node of the collaborative group
transmitting first data outside the group and the first node
transmitting second data inside the group. By using different MAC
addresses, the transmission outside the group does not affect
transmission/s inside the group and permits inserting a legacy node
in a group communication. In particular the access scheme remains
synchronized in term of backoff counting inside the group. The
nodes of the group can thus continue collaborating while the nodes
outside the group remains independent and do not cooperate with
each other. The method is compliant with the 802.11 CSMA/CA
standard. In a particular embodiment the first node is the source
node. So the method advantageously allows a node of the
collaborative group issuing a single medium access request to
transmit first data to a legacy node outside the group and to
transmit second data inside the group. According to another aspect
of the invention there is provided a method of data exchange on a
wireless communication medium accessible by a plurality of nodes
via a contention mechanism, the plurality of nodes comprising a
collaborative group of nodes, each node of the collaborative group
being provided with a first and a second MAC address, and,
[0019] upon detection by a second node of the group of a medium
access request containing a second MAC address as source node
address or a medium access authorization containing a second MAC
address as destination node address, the method comprising:
[0020] transmitting first data from a source node to a node outside
the group using said second MAC address as a source address,
and
[0021] transmitting second data from the second node inside the
group using its first MAC address as a source address.
The method allows a source node of the collaborative group
transmitting first data outside the group and the second node
transmitting second data inside the group. By using different MAC
addresses, the transmission outside the group does not affect
transmission/s inside the group and permits inserting a legacy node
in a group communication. In particular the access scheme remains
synchronized in term of backoff counting inside the group. The
nodes of the group can thus continue collaborating while the nodes
outside the group remains independent and do not cooperate with
each other. The method is compliant with the 802.11 CSMA/CA
standard. In a particular embodiment the second node is the source
node. So the method advantageously allows a node of the
collaborative group detecting a particular medium access request or
authorization to transmit first data to a legacy node outside the
group and to transmit second data inside the group. In one
embodiment the transmitting of the second data is realized from at
least one node of the group to another node of the group. This
feature allows a plurality, even all, nodes from the group to
transmit (second) data using the same communication opportunity. In
an embodiment a time slot is requested by a medium access request
(RTS) and granted upon a medium access authorization (CTS), the
first and second transmission being realized within the granted
time slot. These features allow optimizing the usage of the granted
time slot by sharing it for the two transmissions. In a particular
embodiment the first data transmission is separated from the second
data transmission by a short control frame enabling the legacy node
to interpret that second data is not destined to it. In a further
embodiment the short control frame communicates to the nodes of the
group the time remaining from the granted time slot for the second
data transmission. This allows optimizing the usage of the time in
the granted time slot in a simple way. In still a further
embodiment a MAC address used as destination address of the short
control frame is changed to the first MAC address of a node of the
collaborative group. This allows to simply directing the message to
the collaborative group. It also indicates that the first data
transmission period is terminated. In a particular embodiment, upon
detection of a medium access request or authorization containing a
second MAC address as a source address, at least one node of the
group prepares second data to be transmitted inside the group in
the said allocated time slot. These features allow the node to be
ready to transmit second data at the time it will get the
authorization to transmit. In still a particular embodiment, upon
detection of a medium access request or authorization containing a
second MAC address, the node having the second MAC address prepares
first data to be transmitted to the node outside the group. These
features allow the source node to be ready to transmit data at the
time it will get the authorization to transmit. These features
apply also to the node having the requested of the current granted
time slot. In one embodiment, the first MAC address is used to
communicate exclusively inside the group of nodes or exclusively
outside the group whereas the second MAC address is used to
combined communication inside and outside the group of nodes. It is
therefore guaranteed that the MAC addresses are representative of
the type of communication, in particular the second MAC address is
representative of the mixed communication scheme (or hybrid mode)
according the invention. In an embodiment, the first address and
second MAC addresses of the node of the group are representative of
a same Media Access Control (MAC) entity. Therefore, the same
component can advantageously be used as the MAC entity for each
nodes of the group. In a specific embodiment, the first and second
MAC addresses are identified by managing an universally/locally
bit. Therefore, the same base of MAC address can advantageously be
used, with only one differentiating bit, in order to ease MAC
address modification and type detection. In one embodiment, all the
first and second MAC addresses are exchanged and/or stored among
the collaborative group. These features enable each node of the
group to indemnify the type of communication (inside or outside the
group). In a particular embodiment, the plurality of nodes
implement a back-off counting procedure to access the wireless
medium, and the collaborative group of nodes implements a
synchronized back-off counting such that each node of the group has
a distinct back-off value. Further, the back-off counting is
synchronized in each node of the group by managing a list of
back-off values of the nodes of the group. These features guarantee
that the nodes of the group remains synchronized in term of
back-off counting, resulting in that a unique node of the group
issue a medium access request at a given time, avoiding therefore
collision for medium access requests inside the group. The
invention also pertain to a computer program comprising
instructions for carrying out each step of the method when the
program is loaded and executed by a programmable apparatus as well
as an information storage means readable by a computer or a
microprocessor storing instructions of a computer program, wherein
it makes it possible to implement the method. The invention further
pertain to a node for data exchange on a wireless communication
medium accessible by a plurality of nodes via a contention
mechanism, the plurality of nodes comprising a collaborative group
of nodes, each node of the collaborative group being provided with
a first and a second MAC address, the node comprising:
[0022] a back-off management module for detecting a successful
contention,
[0023] a RTS/CTS module for determining if a communication from a
source node of the group to a node outside the group is
required,
[0024] a MAC address management module for switching between the
first and the second MAC addresses of the source node as source
address for issuing a request to access the medium by the RTS/CTS
module, according to the determination of the RTS/CTS module.
The invention also pertain to a node for data exchange on a
wireless communication medium accessible by a plurality of nodes
via a contention mechanism, the plurality of nodes comprising a
collaborative group of nodes, each node of the collaborative group
being provided with a first and a second MAC address, the node
comprising:
[0025] a RTS/CTS module for detecting a first or second MAC address
type in a medium access request as source node or in a medium
access authorization as destination node address,
[0026] a data transmission module for: [0027] transmitting first
data to a node outside the group using the second MAC address, and
[0028] transmitting second data inside the group using the first
MAC address.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The invention will now be further explained by reference to
the drawings:
[0030] FIG. 1 illustrates a standard wireless medium access
mechanism;
[0031] FIG. 2 illustrates a communication system capable of
implementing embodiments of the current invention;
[0032] FIG. 3 illustrates a communication apparatus for a
transmitting or receiving node adapted to incorporate the current
invention;
[0033] FIG. 4 illustrates a collaborative group back-off slot
positioning;
[0034] FIG. 5a illustrates a collaborative group communication
timeline, without legacy communication;
[0035] FIG. 5b illustrates a collaborative group communication
timeline including a legacy communication according to an
embodiment of the invention;
[0036] FIG. 6 illustrates a high level algorithm performed by a
peer node of the collaborative group accessing the medium, in order
to support the communication timeline according the FIG. 5b;
[0037] FIG. 7 represents algorithms according to an embodiment of
the invention performed at a peer node of the collaborative
group;
[0038] FIG. 8 illustrates an algorithm according to an embodiment
of the invention performed at a peer node upon receiving a RTS
frame; and,
[0039] FIG. 9 illustrates additional means which may be implemented
in accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] FIG. 1 depicts a standard access mechanism, facilitating
access to a wireless medium for a node. The back-off procedure is
one of the first processes to be implemented.
The figure illustrates the behavior of three groups of stations:
source node 30, destination node 31 and other nodes 32. Upon
starting the back-off process prior to transmitting data, a station
e.g. source node 30 initializes its back-off time counter to a
`random value` as explained above. The back-off time counter is
decremented once every time slot 360 interval for so long as the
channel is sensed idle (count down is starting from T0, 33 as shown
in FIG. 1), `frozen` or suspended when a transmission is detected
on the channel (count down is stopping at T1, 34 as shown in FIG.
1), and reactivated when the channel is sensed idle again (as
example at T2, 35 as shown in FIG. 1). When its back-off time
counter reaches zero 36, the timer expires and then reinitializes
39. The station 30 transmits a data message, e.g. comprising RTS
message 310, which contains the address of the receiver e.g.
destination node 31 and the duration for which the medium is to be
reserved for that message. Source node 30 expects to receive a CTS
message 320 from destination node 31 before transmitting data 330.
The messages are spaced using a SIFS (short inter-frame space) time
interval 37, as required by the protocol. The time unit in the
802.11 standard is the slot time called `aSlotTime` parameter. This
parameter is specified by the PHY (physical) layer (for example,
aSlotTime is equal to 9 .mu.s for the 802.11n standard). All
dedicated space durations are multiple of this time unit. The short
inter-frame space 37 (SIFS) is used to separate a response frame
from the frame that solicited the response, for example between a
data frame and the acknowledgement response (for example, SIFS is
equal to 16 .mu.s for the 802.11n standard). The DCF inter-frame
space (DIFS 38) defines the minimum waiting time for a transmitting
node before trying to transmit some data (DIFS=SIFS+2* aSlotTime).
A collision occurs when two or more stations start transmission
simultaneously (e-g when their own back-off counter has reached
zero nearly at the same time). Ideally, a consistent number of
slots 360 are seen as being expired by all nodes forming the 802.11
cell, e.g. during a back-off countdown procedure 370. As the
CSMA/CA protocol does not rely on the capability of the stations to
detect a collision by hearing their own transmission of data 330, a
positive acknowledgement 340 (ACK) is transmitted by the
destination station 31 to signal the successful packet reception.
The ACK 340 is immediately transmitted at the end of the packet,
after a period of time equivalent to the SIFS 37. If the
transmitting station does not receive the ACK 340 within a
specified ACK Timeout, or it detects the transmission of a
different packet on the channel, it reschedules the packet
transmission according to the given back-off rules. Collision
avoidance is specifically enhanced by the four-way handshaking
mechanism of RTS/CTS 310, 320 exchange, which is a recommended
option of the 802.11 standard. FIG. 1 illustrates such a medium
access protection scheme but it should be noted that the RTS/CTS
handshake is optional in the standard and it is possible the
exchange between nodes comprises only data 330 and ACK 340.
Usually, according to 802.11 standard, to protect transmissions
from collisions, a station begins a transmission sequence with an
RTS/CTS exchange 310, 320: a node 30 will issue a Medium access
request (called Request-to-send, or RTS 310) to a destination node
31, when the sender node aims to transmit data on the 802.11
medium. The duration specified in the RTS 310 is the duration of
the entire exchange including the control packets (that means
including RTS/CTS message exchange) and subsequent data packets.
When the intended receiver destination node 31 receives the RTS
310, and senses the medium to be free, such destination node
replies a Clear-to-send (CTS 320) message after waiting for one
SIFS 37 period, thus acknowledging the request and so accepting
receiving data. The CTS 320 also contains the duration of the
entire exchange from that point of time. The transmitter source
node 30 upon receiving the CTS 320 transmits the DATA 330 packet
after an SIFS 37 period. The receiver responds back with an ACK 340
after a SIFS 37 period following its complete receipt of the DATA
330 packet. Each wireless node maintains a data structure called
the network allocation vector or NAV to store the aggregate
duration of time it knows that the medium would be busy. For
example, the NAV associated with the RTS 310 and CTS 320 are
illustrated, labeled 355 and 350 respectively. Any node (e.g.
others 32 on FIG. 1) hearing a packet not destined for itself, sets
its NAV for the time duration mentioned in the packet header, which
is equal to the time required to transmit all control and data
packets. Access for the other nodes 32 is deferred 40 by suspending
41 their associated timer and then later resuming 42 the timer when
the NAV has expired. This prevents these other nodes 32 from
transmitting any packets during the period the NAV is set. It is
possible that the destination node 32 does not receive the RTS 310
correctly because of a collision or fading. Even if it does, it may
not always respond with a CTS 320 because, for example, the NAV is
set. In any case, the transmitter goes through the random back-off
and retries. The RTS/CTS mechanism is very effective in terms of
system performance, especially when large packets are being
transmitted, as it reduces the length of the frames involved in the
contention process. In fact, assuming perfect channel sensing by
every station, collision may occur only when two (or more) packets
are transmitted within the same slot time. If both transmitting
stations employ the RTS/CTS mechanism, collision occurs only on the
RTS frames, and it is early detected by the transmitting stations
by the lack of CTS responses. According 802.11 standard, the data
frame 330 is unique and unicast (one source and one
destination).
[0041] FIG. 2 shows an example of a communication system where the
present invention can be implemented. In a network using a CSMA/CA
channel access mechanism (for example a wireless network
implementing the 802.11 standard or an equivalent standard of that
type), several nodes 201, 202, 203, 204, 205, 206, 207 exchange
data packets through a transmission channel 200 that may drop or
corrupt the data packets.
Nodes can be divided into two groups: a first group of Nbi nodes
201 to 203 (where i is an integer between 1 and 3) implementing the
802.11 standard, also called legacy stations, and a second group of
Ncj nodes 204 to 207 (where j is an integer between 1 and 4)
implementing the 802.11 standard and an embodiment of the
invention. The second group of node is also called the
collaborative group. Data exchange among Nbi legacy nodes and Ncj
collaborative nodes is managed through standardized 802.11n MAC/PHY
layers.
[0042] FIG. 3 is a block diagram illustrating a schematic
configuration of a communication apparatus 300 representing a
transmitting node or a receiving node adapted to incorporate
embodiments of the invention. The PHY (physical) layer block 303 is
in charge of formatting data packets and sending data packets on
the wireless medium. The MAC layer block 302 is composed of a
standard MAC 802.11 layer 304 and four additional blocks
implementing the invention: [0043] node data transmission block 305
in charge of exchanging data packet with the PHY layer and the
application layer [0044] RTS/CTS modules 306 in charge of managing
Request-To-Send (RTS) and Clear-To-Send (CTS) messages [0045] MAC
address management module 307 capable of implementing an embodiment
of the current invention, [0046] back-off management module 308
implementing the back-off management. The application layer block
301 facilitates application generating and receiving data packets,
for example video data flows.
[0047] FIG. 4 illustrates the collaborative group back-off slot
positioning according to an embodiment of the invention.
While targeting an improved communication service on top of
classical 802.11 type CSMA/CA (such as a TDMA communication for
example), attention of the inventors has been directed on the
grouping of a set of peer nodes among a 802.11 legacy environment
to allow a collaborative medium access. TDMA here refers to a time
division multiple access communication method used in conjunction
with the 802.11 type MAC standard. More precisely, medium access
collaboration is performed by watching the `random values` used to
initialize the back-off time counters among the group, in order
that no back-off time count duplication occurs. Each node may
generate a virtual local image of its peers back-off time counters
values by computing the back-off time of each of its peers, or have
access by other means to said back-off values. Each node manages
its own back-off time. Thus, each node of the group can predict the
back-off time values of its peers and would attempt to access the
wireless medium in a distinct back-off slot, avoiding any access
collision among the group of peer nodes. FIG. 4 illustrates this
concept, in consideration of numbering any back-off slots 360
occurring in a CSMA/CA cell. The idea comprises spreading the
allocation of back-off counts among the group of peer nodes to give
a collaborative group back-off positioning 430. This is effected by
positioning the back-off time expiration of each node of the
collaborative group in a different slot number (as example, by
considering an absolute scale of back-off slots, the current
back-off count being number `n` 400, the scheme would select `n+3`
410 and `n+10` 420 for two distinct peer nodes). The sharing of
back-off slot positioning information may be performed either by
messaging on the wireless channel, or in a preferred embodiment by
pseudo-random generation of a next back-off slot computation
according to the collaborative group back-off slot positioning
scheme of an embodiment of the invention. The count of expired
back-off slots (said going from n to n+1) is performed by wireless
channel spying by each node of the collaborative group, whereby all
collaborative nodes can see the medium activity (mainly idle and
busy periods). The sharing of back-off slot positioning information
allows the collaborative nodes to synchronize their access to the
medium and avoid collisions. However a communication with a legacy
node outside the group risks introducing randomization effects on
the back-off counters which are setup among the group, leading to
back-off de-synchronization inside the group.
[0048] FIG. 5a illustrates a collaborative group communication
timeline, without legacy communication.
With conventional wireless systems using techniques to provide
medium access of the CSMA/CA type, only one particular node is
allowed to transmit data during a specified period of time.
Moreover, each node gets access to the medium randomly. Thus, such
a random, performed on a station basis, allocation provides an
inefficient use of the medium, which might become particularly
critical when the node belongs to a group of nodes exchanging
highly interactive data. Indeed, the communication between two
nodes of the same group may be interrupted by an access to the
medium by a legacy node not belonging to the group. It results
that, the overall efficiency of the communication within the group
is affected. According to an embodiment of the invention there is
provided a collaborative access method or protocol for accessing a
communication medium used by a plurality of communication
terminals, comprising a medium allocation scheme for several nodes
of a collaborative group at a time. A collaborative node of the
group Nci (204 to 207) may request access to a shared medium
according to a legacy protocol, and upon grant of access, the node
may communicate during a transmission opportunity TXOP 40 with one
or more remote nodes according to a collaborative protocol (e.g. by
using a TDMA access scheme). This collaborative protocol may
support a high data rate, a high bandwidth physical layer transport
mechanisms, or other modulation techniques different from the
legacy protocol. As a result, this scheme avoids unnecessary waste
of time in polling, contention, etc. due to the inherent IEEE
802.11 medium, by providing a method for contenting an IEEE 802.11
medium access timeslot and transmitting inside that timeslot in a
different scheme. When a node of the group is granted access to the
communication medium, it may allocate a part of its access time
slot 50 to other nodes in the group. In the present example of FIG.
5a, the access time slot 50 is shared into four timeslots S1, S2,
S3 and S4 (530) allowing data exchange between nodes Nc1, Nc2, Nc3
and Nc4 of the collaborative group. The timeslots 530 may have
different durations and/or different distributions. The xIFS 51 is
a guard time interval between timeslots 530. The maximum limit for
the guard time intervals is shorter than a SIFS so as not to let
any IEEE 802.11 legacy node detect a change of medium talker during
the TXOP 40 duration. Thus time slot period 50 is interpreted as a
single data period, like data frame 330, by a legacy node. As
reminder, a SIFS (Short Inter Frame Space) is used to separate
individual frames in the IEEE 802.11 standard without the
inter-frame interval being interpreted by the nodes as a change of
medium owners. As illustrated in FIG. 5a, a RTS message 310 is
issued by the node Nci of the collaborative group which back-off
count comes to zero (as example NC1), and such RTS message is
indifferently addressed to any other node of the group (as example
NC2, or Nc3 or Nc4). The addressed node will reply with a
corresponding CTS message 320, destined to the RTS emitter
node.
[0049] FIG. 5b illustrates a collaborative group communication
timeline similar to FIG. 5a, including a legacy communication
according to an embodiment of the invention.
The idea here is to allow a legacy communication (preferably in
advance to) and the collaborative communication inside a same CSMA
transmission opportunity TXOP 40. To do so, the collaborative nodes
must detect a legacy timeslot 52 prior to collaborative access time
slot 50. Therefore the proposed scheme jointly supports a standard
MAC frame addressing to legacy node (so that legacy nodes are able
to interpret the legacy communication slot 52) and a collaborative
communication (such that legacy nodes interpret the collaborative
slot 50 as a non-activity period, and so that the collaborative
group communicates in slot 50). Such a communication scheme will be
called "mixed-mode" scheme. According the explanations related to
back-off count management inside the collaborative group (FIG. 4),
any peer nodes (indifferently Nc1, Nc2, Nc3 or Nc4) can issue the
RTS 510 for requesting an access to the medium. In order to be
compliant with legacy communication, the RTS should be standard
compliant and addressed to a legacy node Nbi (Nb1 201 to Nb3 203).
So, the present embodiment proposes maintaining for each peer node
of the collaborative group a set of two distinct MAC addresses (MAC
stands for Medium Access Control), which are representative of this
node in context of either internal (inside the collaborative group
only) or external (including legacy node) support of communication.
Following the requirement to communicate with a legacy node, a peer
node uses either one of its two addresses when accessing the medium
(RTS) through the synchronized collaborative protocol. Let's call
these two MAC addresses MAC type 1 address (or MAC1) and MAC type 2
address (or MAC2), respectively for collaborative group only and
legacy support communications (an alternative of using two separate
MAC addresses is provided in regards to FIG. 9). All the MAC1 and
MAC2 addresses are exchanged and stored among the collaborative
group, for example while performing a group joining procedure (not
detailed here). The two MAC addresses of each node are inserted
into lists containing all MAC1 and MAC2 addresses of the peer
nodes. The list is stored in a memory of each node of the
collaborative group. In order to keep benefit of back-off
synchronization within the collaborative group (for avoiding
collisions), the usage of legacy scheme (FIG. 1) for any of
collaborative peer node issuing data to a legacy node should be
avoided. It is therefore proposed that peer devices use a first
type MAC address for collaborative proprietary communication and a
distinct second type address when talking in a mixed mode as
represented in FIG. 5b. The second type MAC address will be the one
exported to and discovered by legacy devices. Upon issuing of an
access request (RTS 510) on the 802.11 medium, when a legacy slot
is required, a peer node uses the MAC address of the legacy node as
destination MAC address of the RTS frame, and its MAC type 2
address as source MAC address of the RTS frame. The access is
acknowledged (CTS 520) by the targeted legacy node. Using of the
MAC type 2 address from a peer node of the group as source address
in incoming RTS frame introduces a differentiating point. This
supports interpretation by the other peer nodes of a mixed-mode
scheme. The interpretation requires the collaborative nodes to
analyze the MAC source address of any incoming RTS frame (not only
the destination address) in order to determine if the pending
transmission opportunity TXOP 40 (or at least part of it 52) is
targeted to them or to a legacy node. In addition, in order to keep
compliance with the collaborative medium access protocol, as the
peer device accessing the medium is not fixed among the group, an
additional means is provided to masquerade a peer MAC address
requesting legacy communication (here Nc1 205) by MAC address of a
peer having its back-off to 0 (here the peer which masquerades Nc1
MAC address may indifferently be node Nc2 or Nc3 or Nc4). This
would let more often legacy communication opportunity, even if Nc1
has not taken the medium request. In order to be more compliant
with 802.11 standard, it is advised to use a short control frame
550, between legacy communication slot 52 and TDMA communication
slot 50, in order to let legacy device(s) know the remaining
transmission opportunity TXOP that will be granted to other
devices. This may be performed through the 802.11 Reverse Direction
protocol, intended for allowing several exchange sequences within a
single TXOP addressed to different recipient(s). As we mix legacy
330 then proprietary 530 data in a same 802.11 transmission
opportunity TXOP, granted by the collaborative group, the legacy
node will be able to decode first data 330 (targeted to it) and
then to interpret that second data 530 is not destined to it
(thanks to the short control frame 550). FIG. 6 illustrates a high
level algorithm performed by a peer node of the collaborative group
accessing the medium, in order to support the communication
timeline according the FIG. 5b. The peer node ready to access the
medium is any node `Nci` of the group having its back-off count
down to zero, and will be further called the `sender` peer node or
the first node. In case of positive determination 610 that some
data have to be sent to a legacy node from a collaborative peer,
the algorithm can be performed further. The destination MAC address
is determined as the selected legacy node's MAC address. Any
scheduling scheme may be used to do such a selection. In step 620,
a MAC2 address is selected as the source MAC address of the RTS
frame to be issued. As the RTS sender peer device performing steps
610 to 660 is not fixed among the group (the sender peer is the
node of the group having next back-off count down to zero), such
sender peer has to masquerade as having the MAC2 address of the
collaborative peer (from step 610) requesting legacy communication.
Therefore the RTS sender peer uses the MAC2 address of peer having
data to transmit (that is the "source" peer) to a legacy node. At
630, the RTS frame is prepared and then sent to other nodes through
the medium by the sender peer. In accordance with the embodiment of
FIG. 5b, the sender peer transmits a RTS frame 510 with a duration
field greater than required for the legacy transmission to prevent
transmission by other legacy stations during the slot 50 sequence
dedicated to data exchange inside the collaborative group. RTS
frame's duration field contains value in microseconds of time
needed to transmit legacy data 330 plus collaborative group data
530. The network allocation vector (NAV) of other legacy stations
will be set accordingly to cover the transmission opportunity TXOP
time 40 when receiving the RTS frame. At 640, the sender node waits
for the end of the legacy communication 52. In step 650, the sender
peer node sends a control frame 550 which indicates the end of
communication for the legacy node and the subleasing of the
remaining time for other communications. In a preferred embodiment,
a short frame according the 802.11n "reverse direction" (RD)
feature is used. With RD, once the transmitting sender peer station
has obtained the transmission opportunity TXOP 40, it may grant
permission to other station to send information back during its
TXOP. The sender peer is seen as a RD initiator, and sends its
permission to a RD responder node using a Reverse Direction Grant
(RDG) in the RDG/More PPDU field of the HT Control field in the MAC
frame. This bit is used by the RD initiator for granting permission
(RDG) to the RD responder, and it is used by the RD responder to
signal whether or not it is sending more frames immediately
following the one just received. According the RD protocol, during
an RD exchange sequence, the RD initiator station may transmit
PPDUs and obtain response PPDUs from a single station (RD
responder) during the exchange. As a result, in an optional
embodiment, the control frame 550 is not used but the first slot S1
530 embeds the Reverse Direction Grant (RDG). This mode is
preferably set when the sender peer is currently the source peer of
the determined legacy flow. In step 660, the MAC address used as
destination address of the control frame 550 (or optionally the
first slot S 530) is changed to the MAC addresses of type 1 of one
node of the collaborative peers. Further, each peer node waits for
its TDMA slot 530 in order to convey data according to the
collaborative communication scheme. FIG. 7a illustrates a legacy
flow admission according to an embodiment of the present invention
performed by a collaborative peer node upon admitting a new legacy
flow. Upon discovery of a request to emit data flow to a legacy
device at 700, each node Nci has to detect at 701 if the
collaborative group is active. The group is considered active if
data have to be transmitted inside the group. Several known
utilities support how to detect an incoming legacy flow can be
performed. As examples, Generic Advertisement Service (GAS) which
provides for Layer 2 transport of an advertisement protocol's
frames between a mobile device and a server in the wireless
network; also upper high layer protocols, like UPnP for "Universal
Plug and Play" network protocol promoted by the UPnP Forum, etc. In
case the collaborative group is not active (701 negative) and if
the node checks it is the source of the legacy flow (703 positive)
the node sets to a legacy mode. In case the collaborative group is
active (701 positive) the node sets to a hybrid mode. Flow
schedulers are present at each collaborative node associating a
mode flag to each incoming flow in order to keep in memory the used
mode (hybrid or legacy) for the flow. FIG. 7b illustrates the
algorithm performed by a sender peer node Nc of the collaborative
group upon accessing the medium. The algorithm is executed when the
back-off counter of a sender peer node expires 710. The sender node
first checks if it pertains to an active collaborative group 720.
If this is not the case, the node uses a 802.11 legacy protocol,
which is the unicast communication targeted to the legacy node. To
do so, the sender node uses its MAC1 type address as source of RTS
frame, and the MAC address of the legacy device as destination
address. If the test 720 is positive, the node uses either a
collaborative communication scheme 50 according to FIG. 5a or a mix
mode scheme according FIG. 5b. To distinguish between the two
cases, the step 610 for determining a legacy communication presence
is mainly composed of two tests. First to detect in a flow
scheduler table the presence of an admitted flow labelled as an
HYBRID mode. If such a label is absent, the collaborative
communication scheme 50 of FIG. 5a is performed in step 740. If
such a label is present, the mixed-mode scheme of FIG. 5b is
applied: a second test 741 consists in determining if the sender
peer node is the source of the detected admitted hybrid flow, in
order to further obtain the correct MAC2 type address to use as
source MAC address in the RTS frame. If the source peer node is the
sender one (741 positive), the MAC2 type address is its proper one.
If the source peer is not the sender node (741 negative), the MAC2
type address of the source peer node corresponding to the detected
admitted hybrid flow is extracted from its memory and spoofed by
the sender node 750. After these steps, the sender node prepares
its hardware to use the determined MAC2 address 751. Then the
medium access is performed at 630 using the determined MAC
address.
[0050] FIG. 8 illustrates the decisions performed at a peer node of
the collaborative group receiving a RTS frame, in order to decide
on which communication scheme the current frame exchange will
rely.
In step 800, a RTS frame 310,510 is received by a receiving peer
node of the group. The receiving node checks 810 whether the MAC
source address of the RTS frame belongs to the MAC1 or MAC2 list of
the group. If this is not the case, the frame originates from a
legacy device, which follows the 802.11 standard protocol, so the
algorithm ends at step 850 by following a legacy protocol (as
example, by setting its NAV if it is not the destination of the RTS
frame). If the check 810 is positive (the found MAC source address
corresponds to a peer, 811 and 812 check the type of MAC address
used, and redirect to step 830 if a MAC2 type address is used,
otherwise to 820 if a MAC1 address is used. Going to test 820, a
receiving peer node should only communicate via collaborative
scheme, so that the destination address specified in the RTS frame
should be part of MAC1 address of a peer. If this is the case, then
the communication scheme to be followed is the collaborative scheme
840 of FIG. 5a. In case the MAC address used in the destination
address specified in RTS frame is unknown in the group (test 820
negative), then the sender peer is considered as fault because it
has used the collaborative medium access for a legacy communication
(the effect we want avoid) and it is banned from the group at 821.
If the test 812 result is negative, MAC2 type address is used, then
the mix communication scheme as described in regards with FIG. 5b
is used. The receiving peer is now aware of the communication
scheme to use. It has further to determine if it is allowed to send
data, according to the flow considered for the legacy timeslot 52.
The flow determination (step 830) consists in retrieving which node
is linked with MAC2 address of the source MAC address of the
received RTS frame. If the address corresponds to the address of
the receiving node (830 positive), step 831 is executed, consisting
in waiting for the CTS frame 520 (from legacy node) before issuing
the data flow 330 on the medium to legacy node destination. The
other receiving nodes for which test 830 result is negative,
execute step 832, consisting in waiting for the collaborative
timeslot 50 to start.
[0051] FIG. 9 represents an IEEE 802 48-bit address space
illustrating a particular way of designing the MAC1 and MAC2 type
addressing concept.
Although intended to be a permanent and globally unique
identification, it is possible to change the MAC address on most
modern hardware. As example, changing MAC addresses is necessary in
network virtualization. It can also be used in the process of
exploiting security vulnerabilities. It is proposed to distinguish
between MAC1 and MAC2 addresses, as is explained hereafter. IEEE
Std 802.11 has chosen to use the IEEE 802 48-bit address space
(defined in 5.2 of IEEE Std 802-1990), which is represented as a
string of six octets (see FIG. 9). The octets are displayed from
left to right, in the order that they are transmitted on the LAN
medium, separated by hyphens. Each octet of the address is
displayed as two hexadecimal digits. The bits within the octets are
transmitted on the LAN medium from left to right. In the Binary
Representation the first bit transmitted, of each octet, on the LAN
medium is the least significant bit of that octet (b1). Addresses
can either be universally administered addresses or locally
administered addresses. Universally administered and locally
administered addresses are distinguished by setting the
second-least-significant bit of the most significant byte of the
address (900). This bit is also referred to as the U/L bit, short
for Universal/Local, which identifies how the address is
administered. If the bit is 0, the address is universally
administered. If it is 1, the address is locally administered.
[0052] A universally administered address is uniquely assigned to a
device by its manufacturer; these are sometimes called burned-in
addresses. The first three octets (in transmission order) identify
the organization that issued the identifier and are known as the
Organizationally Unique Identifier (OUI). The following three
octets are assigned by that organization in nearly any manner they
please, subject to the constraint of uniqueness. [0053] A locally
administered address is assigned to a device by a network
administrator, overriding the burned-in address. Locally
administered addresses do not contain OUIs. In this particular
embodiment, it is proposed to keep relying on the universally
administered address, but to manage the usage of the U/L bit in
order to distinguish between MAC1 or MAC2 type addresses (in
regards to collaborative group according the invention). As
example, U/L bit 900 is set to 1 for emulating a MAC2 type
according the invention.
* * * * *